1. Field of the Invention
The invention relates generally to pattern assemblies for the lost foam casting process. More particularly, the invention relates to lost foam pattern assemblies for intake manifolds for two-stroke engines.
2. Reference to Prior Art
Shown in FIGS. 1 through 4 of the drawings is a prior lost foam pattern assembly 11 for an intake manifold (not shown) for a two-stroke internal combustion engine (not shown).
The pattern assembly 11 corresponds essentially identically to the resulting intake manifold and includes four fuel/air mixture passages 13 which, in the assembled engine, extend from four carburetors (not shown) to four crankcases (not shown) in an engine block (not shown).
The pattern assembly 11 includes a first or engine block mounting surface 15 adapted to engage the engine block and having therein four generally rectangular openings 17.
The pattern assembly 11 also includes a second or carburetor mounting surface 19 which extends in spaced generally parallel relation to the first or engine block mounting surface 15 and which includes four generally indentical circular openings 21.
The four fuel/air mixture passages 13 extend between the circular openings 21 in the carburetor mounting surface 19 and the rectangular openings 17 in the engine block mounting surface 15.
The fuel/air mixture passages 13 are generally identical and each includes (See FIGS. 2 and 3) a rectangular portion 31 extending inwardly from the associated rectangular opening 17 in the engine block mounting surface 15 and including a transverse reed valve mounting surface 33 which, in the assembled engine, engages and supports a reed valve (not shown) and which extends generally parallel to the mounting surfaces 15 and 19 and has therein a second rectangular opening 35 of somewhat smaller size than the rectangular openings 17 in the engine block mounting surface 15. The rectangular opening 35 in the reed valve mounting surface 33 is defined by two long side edges 37 and 39 and two end edges 41 and 43. The side edge 37, when projected perpendicularly to the carburetor mounting surface 19, approximately bisects the associated circular opening 21, and the other side edge 39 lies outside the periphery of the associated circular opening 21.
The rectangular portion 31 of each fuel/air mixture passage 13 is also defined by two long side walls 47 and 49 and two short end walls 51 and 53. The long side wall 49 and the short end walls 51 and 53 extend at an obtuse angle with respect to the engine block mounting surface 15. In the disclosed construction, the angle is slightly larger than 90.degree.. The other long side wall 47 defines an acute angle of somewhat less than 90.degree. with respect to the engine block mounting surface 15 and thus defines (See FIG. 3) an undercut area 61 with respect to a die member (not shown) moving in a direction perpendicularly to, and away from, the engine block mounting surface 15.
Each fuel/air mixture passage 13 also includes (See FIGS. 1 and 3) a transition portion 71 which extends between the associated circular opening 21 in the carburetor mounting surface 19 and the associated rectangular opening 35 in the reed valve mounting surface 33. The transition portion 71 of each fuel/air mixture passage 13 is defined by first wall means 73 extending from approximately one-half of the periphery of the associated circular opening 21 in the carburetor mounting surface 19 and to the side edge 3 and to the end edges 41 and 43 of the rectangular opening 35 in the reed block mounting surface 33. The first wall means 73 includes suitable draft to facilitate withdrawal of a die member (not shown) perpendicularly to, and from, the engine block mounting surface 15.
The transition portion 71 of each of the fuel/air mixture passages 13 is also defined by second wall means 83 extending from the other half periphery of the associated circular opening 21 in the carburetor mounting surface 19 and to the other side edge 37 of the rectangular opening 35 in the reed block mounting surface 33.
The second wall means 83 extends, in part, radially outwardly of the associated circular opening 21 and to the ends of the side edge 37 of the rectangular opening 35 in the reed valve mounting surface 33, thus defining (See FIG. 1) two additional undercut areas indicated at 85 and 87 and located below the carburetor mounting surface 19.
In addition, the outer or exterior surface 89 of the second wall means 83 extends radially inwardly of the other half periphery of the associated circular opening 21 in the carburetor mounting surface 19, thereby providing a further undercut area 91 associated with each of the fuel/air mixture passages 13.
Accordingly, in order to obtain the pattern assembly 11, the assembly 11 was divided into a base piece 93 defining the engine block mounting surface 15, the four rectangular passage portions 31, approximately one-half of the carburetor mounting surface 19, and the first wall 73 means partially defining the transition portion 71 of the four fuel/air mixture passages 13. The second wall means 83 which defines the transition portion 71 of the four fuel/air mixture passages 13 and the remaining approximately one-half of the carburetor mounting surface 19 were provided by four additional pieces 95 which were glued to the base piece 93 as indicated in FIG. 1 to provide the resulting pattern assembly 11.